Not sure how much really this stories and creatures are famous in your country. But here is it classic and kids from all over Finland want to visit this place.
Unique Suggestions: be sure you take your kids with you.
Fun Alternatives: Link
You surely miss nothing if you do not visit the local museum.
Unique Suggestions: I guess that if you are really unlucky with the weather, on a cold rainy day, that might be the only choice.